This invention relates generally to subsurface well apparatus, more specifically, to apparatus for perforating subsurface earth formations, and particularly to apparatus for firing tubing conveyed perforating apparatus.
It has become common practice in the completion of oil and gas wells to perforate the well casings and the surrounding formations to bring a well into production. One method of providing this capability has a perforating apparatus attached to the end of a tubing string which is lowered and set in place when the perforating apparatus is opposite the formation to be produced. The perforating apparatus may then be detonated and the well placed into production through the tubing strings.
The systems for firing the perforating devices have typically been either an electrical firing system or a non-electric percussion firing system activated by dropping a member through the tubing. Neither method has been entirely satisfactory in the past. Electrical firing systems require care in connecting and running and can be activated from stray electrical currents. In addition, electrical connections can be short-circuited by moisture. Percussion firing systems commonly require a bar member, referred to as a "go devil", be dropped through the tubing string thereby impacting a percussion firing assembly. These percussion firing assemblies typically have some primary explosives in the perforating apparatus while it is affixed to the tubing and lowered into position within the well. As a result of the deficiencies of these systems, accidental and premature firings are a possibility. Further, in the event of a malfunction of these systems there is a need of a suitable back-up method of firing the perforating apparatus.
These and other disadvantages are overcome with the present invention by providing method and apparatus for firing subsurface perforating apparatus using a mechanical operated firing system capable of operation from a "slick line" or other non-electrical cable.